1. Field of the Invention
This invention relates generally to tire monitoring and, more particularly, to a system, method and apparatus for remotely monitoring tires on towed trailers and truck/trailer combinations, for abnormal tire conditions, such as low tire pressure and/or high tire temperature where the receiver need not be reprogrammed when a vehicle changes trailers.
2. Description of the Related Art
The most common cause of low tire pressure and flat tires is puncturing of the tire by a sharp object, such as a nail, which lets air out. Depending on the size of the hole, the tire may deflate slowly or rapidly. Another cause of low tire pressure and/or a flat tire is a failure of or damage to the valve stem through which air in the tire can leak out. Sometimes, low pressure in a tire may be caused by vandalism. Examples of this can be as simple as letting air out through the valve stem, which is easily repairable by simply refilling the tire, or slashing the sidewalls, which may require replacing the tire.
A tire may be damaged in a collision with another vehicle or by an object that causes the rubber of the tire to separate from the wheel, or rips the tire. Excessive wear of the tire tread to the point where even blunt stones or a pot hole in the road may puncture the rubber and cause a slow air leak in the tire.
Tires can leak air due to a variety of reasons. These include, but are not limited to: a damage to the wheel itself, a damaged valve stem, a puncture in the tire, which sometimes may be hard to find if the puncture was caused by an object that didn't embed itself in the tire, such as can happen by running over a board with nails sticking out, and by improper installation of the tire, which could involve the bead of the tire being cut when a tire is being mounted on the rim.
It is also noted that tires lose air over time. A new tire, properly inflated, will lose air even when there is no puncture in the tire. A primary cause for this loss of tire pressure in a new tire is the slow leakage of air through the valve stem. Given enough time, a tire can fully deflate with no obvious or detectable reason.
It is now well known that vehicle tires can, and should, be monitored to avoid unwanted damage due to the occurrence of abnormal tire conditions, two such conditions being, for example, low tire pressure and high tire temperature. Numerous devices have been suggested for monitoring of tires to detect abnormal tire conditions, and, particularly, for monitoring tires to detect low tire pressure.
In the United States, vehicles manufactured after model year 2007 were required to have tire pressure monitoring systems built-in. It is understood that this requirement does not apply to trailers. Aftermarket tire pressure monitors from various companies are available which notify the driver of a vehicle of the tire pressure in each wheel, as well as exactly which tire of the system is being displayed. A much less expensive way to monitor tire pressures is to install valve stem caps that alert the driver to low tire pressure. These work by first setting the pressure on the cap to match the pressure a driver desires for the tires. Once installed on the tire's valve stem, the tip of these caps will change color (from green, to yellow, to red) when the tire becomes under-inflated. Its disadvantages include questionable accuracy, specifically if the caps aren't tightened down enough and the only way to monitor them is from outside of the vehicle by looking directly at the cap.
A much more active approach to monitoring tire pressures involves retrofitting a tire pressure monitor to the vehicle. One such arrangement disclosed in the prior art for sensing tire pressure and temperature is U.S. Pat. No. 5,708,411. In the patent a sensing unit is unattached, it is free floating within the tire casing and is freely movable therein where its movement is normally due to gravity forces when no movement of the tire is occurring and due to centrifugal forces when the tire is being rotated.